Electrical fuse structure and method of formation

ABSTRACT

An embodiment is a fuse structure. In accordance with an embodiment, a fuse structure comprises an anode, a cathode, a fuse link interposed between the anode and the cathode, and cathode connectors coupled to the cathode. The cathode connectors are each equivalent to or larger than about two times a minimum feature size of a contact that couples to an active device.

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/256,792, filed on Oct. 30, 2009, and entitled “Electrical Fuse Structure and Method of Formation,” which application is incorporated herein by reference in its entirety, and U.S. Provisional Patent Application Ser. No. 61/308,588, filed Feb. 26, 2010, and entitled “Electrical Fuse Structure and Method of Formation,” which application is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The disclosure relates generally to a fuse structure and method of forming the fuse structure and, more particularly, to an electrical fuse in a semiconductor device and method of forming the electrical fuse.

BACKGROUND

In the semiconductor industry, fuse elements are widely used features in integrated circuits for a variety of purposes, such as in memory repair, analog resistor trimming, and chip identification. For example, by replacing defective memory cells on chips with redundant cells on the same chips, memory manufacturing yields can be significantly increased. A fuse disconnected by a laser beam is referred to as a laser fuse, and a fuse disconnected by passing an electrical current, or blowing, is referred to as an electrical fuse, or e-fuse. By selectively blowing fuses within an integrated circuit that has multiple potential uses, a generic integrated circuit design may be economically manufactured and adapted to a variety of custom uses.

E-fuses may be incorporated in the design of integrated circuits, wherein the fuses are selectively blown, for example, by passing an electrical current of a sufficient magnitude to cause electro-migration or melting of a fuse link, thereby creating a more resistive path or an open circuit. However, a contact to a cathode of a conventional fuse may cause problems when a large electrical current passes through the fuse. This contact is generally aligned with an axis of a fuse link and nearest to the fuse link and has a very small contact area. Because the contact is nearest to and aligned with the fuse link, the resistance between the fuse link and the contact is much lower than any resistance between the fuse link and any other contacts in the cathode. This low resistance may cause a large proportion of the electrical current to flow through the contact.

The larger electrical current flowing through the contact may cause electro-migration of the metal in the contact to the fuse link. The electro-migration of the metal then may cause the fuse link to short circuit again when the large electrical current was intended to create a more resistive path or open circuit. This problem is increased after a high temperature storage (HTS) or bake process of the chip. Accordingly, there is a need in the art for a more robust fuse structure to overcome the deficiencies of the prior art.

SUMMARY

In accordance with an embodiment, a fuse structure comprises an anode, a cathode, a fuse link interposed between the anode and the cathode, and cathode connectors coupled to the cathode. The cathode connectors are each equivalent to or larger than about two times a minimum feature size of a contact that couples to an active device.

In accordance with another embodiment, a fuse structure comprises an anode, a cathode with connectors coupled to the cathode, and a fuse link coupled between the cathode and the anode. A cross-section area of each of the connectors is equal to or larger than a cross-section area of a connector coupling an active device.

In accordance with a further embodiment, a fuse structure comprises a cathode, a fuse link, an anode, a dielectric over the cathode, openings in the dielectric over the cathode, and metal connectors disposed in the openings. The fuse link is coupled between the cathode and the anode. The openings expose a portion of the cathode, and a cross-sectional area parallel to a top surface of the cathode of each of the openings is greater than a minimum feature size.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present embodiments, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an electrical fuse structure in accordance with an embodiment;

FIG. 2 is an electrical fuse structure in accordance with another embodiment;

FIG. 3 is an electrical fuse structure in accordance with a further embodiment;

FIG. 4 is an electrical fuse structure in accordance with an additional embodiment;

FIGS. 5A-F are an exemplary process to form an electrical fuse structure in accordance with an embodiment; and

FIGS. 6A-F are an illustrative process to form an electrical fuse structure in accordance with a further embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the present embodiments are discussed in detail below. It should be appreciated, however, that this disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.

Embodiments will be described with respect to an electrical fuse structure in a semiconductor chip. Other embodiments contemplate applications where the use of an electrical fuse structure is desirable.

FIG. 1 depicts a fuse structure 10 comprising a cathode 12, a fuse link 14, and an anode 16. The fuse structure 10 may be formed of a metal, such as copper or the like, or silicided polysilicon, such as nickel silicide (NiSi), titanium silicide (TiSi₂), cobalt silicide (CoSi_(x)), platinum silicide (PtSi₂), or the like. Cathode 12 has a rectangular shaped top surface 13 and has two contacts 18 coupled to the top surface 13. Anode 16 has a funnel shaped top surface 17 and has contacts 20 coupled to the top surface 17. The contacts 18 and 20 may comprise copper, tungsten, or metals of the like, and may also comprise a diffusion barrier layer lining the contacts 18 and 20 comprising, for example, TiN, TaN, or the like. The fuse link 14 has a width (perpendicular to arrow 22) much smaller than the width of the cathode 12 and the anode 16. Although the description herein refers to contacts 18 and 20, these contacts may be vias and/or contacts.

Contacts 18 in the cathode 12 couple a larger surface area of the top surface of the cathode 12 than contacts coupling active devices in other portions of the chip, such as to a transistor gate, and the contacts 18 do not align or intersect a longitudinal axis through the fuse link 14 that is represented by the arrow 22. For example, dashed lines 26 illustrate longitudinal axes along edges of the fuse link 14 that define an area in the cathode 12 to which no contacts couple.

As a further exemplary embodiment and to further illustrate the embodiment in FIG. 1, examples of dimensions will be described with respect to a technology node of 32 nm, but the dimensions are not limiting with regard to embodiments described herein. One of ordinary skill in the art will appreciate that the dimensions may be varied according to different technology nodes. In an embodiment in a 32 nm technology node device, the contacts 20 in the anode 16 may be a contact or via, and may have a surface area width of about 40 nm and a length of about 40 nm. Thus, the area of contacts 20 may be square. The contacts 20 are said to be of a minimum feature size, which corresponds to the technology node of the embodiment, such as for gate electrodes, contacts, or metal lines. For example, a contact size may have a critical dimension of between about 15 nm and about 40 nm, and a via size may have a critical dimension of between about 20 nm and about 50 nm, each for a technology node of 32 nm. Thus, the contacts 20 may be equal to or larger than about the minimum feature size of a contact that couples an active device in another portion of the chip, such as to a transistor gate, or further, may be between about one times to about two times the minimum feature size of a contact that couples an active device in another portion of the chip. Minimum feature sizes for different technology nodes will have different critical dimensions.

The fuse link 14 may have a length of approximately 240 nm and a width of between about 40 nm and about 60 nm. Thus, the fuse link 14 width may be equivalent to or larger than about the minimum feature size of a gate electrode, or further, may be between about one times about two times the minimum feature size of a gate electrode. Alternatively, the fuse link 14 width may be equivalent to or larger than about the minimum feature size of a width of a metal line, or further, may be between about one times and about two times the minimum feature size of the width of the metal line. The contacts 18 in the cathode 12 may have a surface area width of about 120 nm and a length of about 120 nm. Thus, the area of contacts 18 may be square, and may be equal to or greater than about two times the minimum feature size of a contact that couples an active device in another portion of the chip, or further, may range from about two times to about four times the minimum feature size of a contact coupling an active device. These dimensions may be varied according to, for example, a different technology node or according to different desires and needs of a design.

The arrow 22 also represents the direction of the flow of electrons when an electrical current is applied to the fuse structure 10. Thus, as is readily apparent to a person having ordinary skill in the art, the contacts 18 are equidistant to the fuse link 14 such that the resistances between the fuse link 14 and each of the contacts 18 may also be equal. The equal resistances may cause the current flowing through the fuse link 14 to be substantially evenly proportioned between each contact 18. This may reduce a large current that may be isolated to a single contact of the prior art. Further, the contact areas of the contacts 18 are substantially larger such that the current density in a single contact 18 may be reduced when an electrical current is applied to the fuse structure. The reduced magnitude of current and current density flowing through any single contact 18 generally causes the fuse structure to have a more robust electro-migration capability such that the metal in or above the contacts 18 are generally less likely to migrate to the fuse link 14 and short the fuse structure 10.

FIGS. 2 through 4 illustrate further embodiments. The embodiments in FIGS. 2 through 4 may be desirable when more contacts are needed for redundancy. FIG. 2 illustrates a fuse structure 30 comprising a cathode 32. The cathode 32 comprises a one-by-four array of inner and outer contacts 34 a and 34 b, respectively, which are referred to collectively as the contacts 34, which may also be vias. The contacts 34 again are not aligned with the fuse link 14 but are offset from the longitudinal axis of the fuse link. The inner contacts 34 a are equidistant from a longitudinal axis of the fuse link 14, or from the area defined by dashed lines 26, and outer contacts 34 b are equidistant from the longitudinal axis. The contacts 34 have a contact surface area that is larger. The contacts 34 may each be approximately 120 nm in length and about 60 nm in width, although other dimensions may be used.

FIG. 3 illustrates a fuse structure 40 comprising a cathode 42. The cathode 42 comprises a two-by-two array of contacts 44, which may also be vias. The contacts 44 again are not aligned with the fuse link 14 and have a relatively larger contact surface area. The two contacts 44 more proximate to the fuse link 14 are equidistant from a longitudinal axis of the fuse link 14, and the two contacts 44 furthest from the fuse link 14 are equidistant from the longitudinal axis. The contacts may each be approximately 60 nm in length and about 120 nm in width, but other dimensions are contemplated within scopes of this embodiment.

FIG. 4 illustrates a fuse structure 50 comprising a cathode 52. The cathode 52 comprises a two-by-four array of contacts 54, which may also be vias. The contacts 54 are likewise not aligned with the fuse link 14 and have a relatively larger contact surface area. Pairs of corresponding contacts 54 are equidistant from a longitudinal axis of the fuse link 14. Contacts 54 are symmetrically arranged on opposing sides of the longitudinal axis of the fuse link 14. The contacts 54 may each be approximately 60 nm in length and about 60 nm in width, but the dimensions may be varied.

FIGS. 5A through 5F illustrate an exemplary method to form a fuse structure in accordance with embodiments. These figures illustrate a cross-section of a cathode of the fuse structure, for example, the cathode 12 in FIG. 1 along line A-A. In FIG. 5A, a semiconductor substrate 102 is provided, such as silicon, silicon-germanium, or the like. A recess is etched in the semiconductor substrate 102, and a dielectric is formed in the recess to create a shallow trench isolation (STI) 104. The dielectric may be formed by oxidizing the semiconductor substrate 102, by depositing the dielectric over the semiconductor substrate 102, or similar techniques.

In FIG. 5B, a metal or polysilicon layer 106 is formed over the semiconductor substrate 102, such as by a blanket deposition. If metal is used, the metal layer 106 may comprise copper or the like. A photoresist 108 is then formed above the metal or polysilicon layer 106 that is above the STI 104. The top surface of the photoresist 108 is patterned similar to the top surface illustrated in FIGS. 1 through 4. The dashed lines in the photoresist 108 indicate the width of a fuse link in the subsequent fuse structure.

In FIG. 5C, an etch process is carried out such that the pattern of the photoresist 108 is imposed on the metal or polysilicon layer 106. The dashed lines in the metal or polysilicon layer 106 show the width of a fuse link coupled to the cathode. If polysilicon is used in the metal or polysilicon layer 106, the polysilicon then may be silicided by depositing a metal, such as titanium, cobalt, nickel, platinum, or the like, and annealing the structure to create titanium silicide, cobalt silicide, nickel silicide, platinum silicide, or other similar silicides. Then, a dielectric layer 110, such as an interlayer dielectric (ILD), is deposited over the semiconductor substrate 102. A photoresist 112 is deposited over the dielectric layer 110 and patterned to expose portions of the dielectric layer 110 over the remaining metal or polysilicon layer 106 through openings 114.

In FIG. 5D, an etch process is carried out to impose the pattern of openings 114 into the dielectric layer 110 to form openings 116. Another photoresist 118 is then formed over the dielectric layer 110 with an opening 120 patterned therein. An isotropic etch is then carried out to form an opening in the dielectric layer 110 so that contacts subsequently formed in openings 116 are coupled together. This process thus describes the use of a dual damascene process. However, embodiments are not limited to this process, and a person having ordinary skill in the art will readily understand the efficacy of a single damascene process or other like processes.

In FIG. 5E, a conformal diffusion barrier layer 122 is deposited over the structure and a metal 124 is deposited over the diffusion barrier layer 122. The diffusion barrier layer 122 may be any known barrier layer, such as titanium nitride, tantalum nitride, or the like. The metal 124 may be copper, tungsten, or the like.

In FIG. 5F, excess metal 124 is removed, and diffusion barrier layer 122 over the dielectric layer 110 that is not within any of the formed openings is removed, such as by a chemical mechanical polish (CMP). Accordingly, contacts 126 are formed coupling the metal or polysilicon layer 106 that is the cathode, and line 128 couples the contacts 126 together and forms an area to which vias in subsequent intermetal dielectric (IMD) layers may be coupled. The contacts 126 thus formed have a larger contact area and are not aligned with any fuse link, as indicated by the dashed lines. This process may result in the layout of the fuse structure 10 as illustrated in FIG. 1, but a person having ordinary skill in the art will readily understand any needed modifications to this process to form other embodiments, such as those in FIGS. 2 through 4.

FIGS. 6A through 6F illustrate another exemplary method to form a fuse structure in accordance with embodiments. These figures illustrate a cross-section of a cathode of the fuse structure, for example, the cathode 12 in FIG. 1 along line A-A. In FIG. 6A, a first dielectric layer 202 is provided, such as silicon dioxide, silicon nitride, silicon oxynitride, or the like. The first dielectric layer 202 may be formed above a semiconductor substrate, such as part of an interlayer dielectric (ILD) or intermetal dielectric (IMD) layer in a semiconductor chip. A photoresist 204 is patterned over the first dielectric layer 202 with opening 206 therein. The opening 206 is patterned similar to the top surface illustrated in FIGS. 1 through 4. The vertical dashed lines in the photoresist 204 indicate the width of a fuse link in the subsequent fuse structure, and the horizontal dashed lines show the top surface of the photoresist 204 around other areas of opening 206.

In FIG. 6B, the first dielectric layer 202 is etched such that opening 206 is imposed into the dielectric layer 202. A metal or polysilicon layer 208 is formed over the first dielectric layer 202, such as by a blanket deposition. If metal is used, the metal layer 208 may comprise copper or the like. Any excess metal or polysilicon is then removed, such as by a chemical mechanical polish (CMP). If polysilicon is used as a polysilicon layer 208, a metal, such as titanium, cobalt, nickel, platinum, or the like, may be deposited over the polysilicon and annealed to form a silicide, such as titanium silicide, cobalt silicide, nickel silicide, platinum silicide, or other similar silicides.

In FIG. 6C, a second dielectric layer 210 is deposited over the first dielectric layer 202 and the metal or polysilicon 208. The second dielectric layer 210 may be a subsequent ILD IMD layer. A photoresist 212 is deposited over the second dielectric layer 210 and patterned to expose portions of the dielectric layer 210 over the remaining metal or polysilicon layer 208 through openings 214.

In FIG. 6D, an etch process is carried out to impose the pattern of openings 214 into the second dielectric layer 210 to form openings 218. Another photoresist 216 is then formed over the second dielectric layer 210 with an opening 220 patterned therein. An isotropic etch is then carried out to form an opening in the second dielectric layer 210 so that contacts subsequently formed in openings 218 are coupled together. This process thus describes the use of a dual damascene process. However, embodiments are not limited to this process, and a person having ordinary skill in the art will readily understand the efficacy of a single damascene process or other like processes.

In FIG. 6E, a conformal diffusion barrier layer 222 is deposited over the structure and a metal 224 is deposited over the diffusion barrier layer 222. The diffusion barrier layer 222 may be any known barrier layer, such as titanium nitride, tantalum nitride, or the like. The metal 224 may be copper, tungsten, or the like.

In FIG. 6F, excess metal 224 is removed, and diffusion barrier layer 222 over the second dielectric layer 210 that is not within any of the formed openings is removed, such as by a chemical mechanical polish (CMP). Accordingly, vias 226 are formed coupled to the metal or polysilicon layer 206 that is the cathode, and line 228 couples the vias 226 together and forms an area to which vias in subsequent IMD layers may be coupled. The vias 226 thus formed have a larger contact area and are not aligned with any fuse link, as indicated by the dashed lines. This process may result in the layout of the fuse structure 10 illustrated in FIG. 1, but a person having ordinary skill in the art will readily understand any needed modifications to this process to form other embodiments, such as those in FIGS. 2 through 4.

Although these embodiments and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 

What is claimed is:
 1. A fuse structure comprising: an anode; a cathode including a region being free of cathode connectors, the region being defined by a first side extending along a first axis and a second opposing side extending along a second axis, the first side and the second opposing side extending an entire length of the cathode; a fuse link interposed between and connecting the anode and the cathode, the fuse link having a first edge extending along the first axis and a second edge extending along the second axis; anode connectors coupled to the anode, the anode connectors each having a first size; and cathode connectors coupled to the cathode, the cathode connectors each having a second size, the second size being greater than the first size.
 2. The fuse structure of claim 1, wherein the cathode connectors are each between about two times and about four times a minimum contact feature size.
 3. The fuse structure of claim 1, wherein the anode connectors are each equivalent to or larger than one times a minimum contact feature size.
 4. The fuse structure of claim 3, wherein the anode connectors are each between about one times and about two times the minimum contact feature size.
 5. The fuse structure of claim 1, wherein a width of the fuse link is equivalent to or larger than about one times a minimum gate electrode feature size corresponding to the technology node of the fuse structure, and wherein a width of the region extending from the first side to the second opposing side is substantially equal to the width of the fuse link.
 6. The fuse structure of claim 1, wherein each of the anode connectors has a surface area that is square; and wherein each of the cathode connectors has a surface area that is square.
 7. The fuse structure of claim 1, wherein the second size of the cathode connectors is larger than about two times the first size of the anode connectors.
 8. The fuse structure of claim 1, wherein each cathode connector of the cathode connectors is equidistant from a longitudinal axis of the fuse link.
 9. A fuse structure comprising: an anode including a plurality of anode contacts, each anode contact of the plurality of anode contacts having a first surface area; a cathode including a plurality of cathode contacts, each cathode contact of the plurality of cathode contacts having a second surface area, the second surface area being larger than the first surface area; and a fuse link disposed between and connecting the anode and the cathode, the fuse link having a first edge extending along a first plane and a second opposing edge extending along a second plane, the first plane being substantially parallel to the second plane, wherein the cathode further includes a region extending from the first plane to the second plane and extending an entire length of the cathode, the region being free of cathode contacts.
 10. The fuse structure of claim 9, wherein the anode has a funnel shaped top surface.
 11. The fuse structure of claim 9, wherein the cathode has a rectangular shaped top surface.
 12. The fuse structure of claim 9, wherein the second surface area is greater than about two times the first surface area.
 13. The fuse structure of claim 9, wherein the first surface area is substantially equal to a minimum feature size corresponding to a technology node of the fuse structure.
 14. The fuse structure of claim 9, wherein the first surface area and the second surface are square.
 15. A structure comprising: an anode including an anode contact; a cathode including: a region being free of cathode contacts and defined by a first side extending along a first axis and a second opposing side extending along a second axis, the first side and the second opposing side extending an entire length of the cathode; a first cathode contact; and a second cathode contact; and a fuse link disposed between and connecting the anode and the cathode, the fuse link having a first longitudinal surface and a second opposing longitudinal surface, wherein the region has a width extending from the first side to the second opposing side, the width of the region being substantially equal to a width of the fuse link extending from the first longitudinal surface to the second opposing longitudinal surface; wherein the first cathode contact and the second cathode contact are equidistant from the first side and the second opposing side, respectively; and wherein each of the first cathode contact and the second cathode contact is larger than the anode contact.
 16. The structure of claim 15, wherein the first cathode contact is disposed away from the region in a first direction; and wherein the second plurality of cathode contacts is disposed away from the region in a second direction, the second direction opposite the first direction.
 17. The structure of claim 15, wherein the first cathode contact and the second cathode contact are symmetrically arranged on opposing sides of the longitudinal axis of the fuse link.
 18. The structure of claim 15, wherein the anode contact is substantially equal to a minimum feature size corresponding to a technology node of the structure.
 19. The structure of claim 15, wherein each of the first cathode contact and the second cathode contact is greater than about two times a minimum feature size corresponding to a technology node of the structure. 